Method and apparatus for compensating reproduced audio signals of an optical disc

ABSTRACT

An apparatus and method for compensating audio signals to be recorded on an optical disc to optimize usage of memory in an audio decoding circuit, and to neutralize invalid audio data to produce good audio quality. A determination is made with regard to whether audio data signals contain normal data or invalid data. Invalid data is adjusted into normal audio data, and stored in the memory. The volume of the data stored in the memory is monitored to detect overflow and underflow conditions of the memory, a data transmitting stopping signal being sent during an overflow condition of the memory, a data transmitting requesting signal being sent during an underflow condition. The audio data reproduced from the memory is decoded, and the decoded audio data is output. Undesired errors are prevented by monitoring the reproduced audio data for invalid data and by adjusting invalid data into normal data when detected.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forreproducing data from an optical disc and, more particularly, to amethod and apparatus for compensating audio signals reproduced from theoptical disc.

[0003] 2. Description of the Prior Art

[0004] A Compact Disc (referred to as “CD” hereinafter) is aconventional recording medium which records data digitally. Because datais recorded digitally, it does not deteriorate when reproduced, even ifthe CD is used repeatedly. However, the CD, which is presently usedthroughout audio and computer fields, has limited recording capacitythat restricts its use in video. A Digital Versatile Disc (“DVD”) hasbeen recently developed as a new recording medium suitable for themulti-media age in the recording media market. The DVD is able to storemoving images as well as numbers, characters, figures and voices. TheDVD has all the advantages of the CD, and has a recording capacity ofabout 5.2 Gbytes per side. Therefore, a complete conventional movie,including moving images, can be sufficiently recorded on one DVD.

[0005] Physically, the DVD is as small and durable as a conventional CD.Furthermore, data stored on the DVD is recorded digitally, rendering itable to be preserved easily. For these reasons, the DVD is analternative recording medium that has become widely used in the marketof recording media including video/audio and computer fields. The wideuse of the DVD in image fields has given the DVD a good reputation as animage recording media.

[0006] Conventional reproduction apparatuses for reproducing video/audiosignals from the DVD, and the operation thereof, are described in detailbelow with reference to FIGS. 1 to 4C of the attached drawings.

[0007]FIG. 1 is a block diagram showing a conventional reproductionapparatus for the optical disc. As shown in FIG. 1, the conventionalreproduction apparatus comprises: an optical disc (i.e. DVD) 1 on whichvideo/audio signal data are recorded; an optical pick-up apparatus 3 forreading the data recorded on the optical disc 1; and a motor 11 forrotating the optical disc 1; and a servo-circuit 13 for controlling themotor 11 and the optical pick-up apparatus 3.

[0008] The conventional reproduction apparatus further comprises: amicroprocessor 15 for managing the overall control of the reproductionapparatus according to a user's request, and for controlling theservo-circuit 13; a navigator 17 for receiving commands from themicro-processor 15, and for executing the commands as to thetransmission of data; and a high frequency amplifying circuit 5 foramplifying data read from the optical pick-up apparatus 3 in highfrequency bands, and for outputting amplified signals under the controlof the navigator 17.

[0009] The conventional reproduction apparatus also comprises: an errorcorrecting circuit (ECC) 7 for correcting errors in bit stream ofamplified signals output from the high frequency amplifying circuit 5and for outputting corrected signals under the control of the navigator17; and a Variable Bit Rate buffer (VBR buffer) 9 for temporarilystoring signals output from the error correcting circuit 7 under thecontrol of the navigator 17. The VBR buffer 9 may be a First In FirstOut (FIFO) buffer.

[0010] In addition, the conventional reproduction apparatus comprises adata decoding unit 20 which is composed of a video decoding circuit 21,a graphics circuit 25 and an audio decoding circuit 27. When the bitstream output from the VBR buffer 9 is input to the navigator 17 and thedata decoding circuit unit 20, the video decoding circuit 21 extractsonly video signal data therefrom and decodes the video signal data basedon data dividing control signals of the navigator 17. Similarly, thegraphics circuit 25 extracts and decodes only caption signal data, andthe audio decoding circuit 27 extracts and decodes only audio signaldata.

[0011] The video data decoded by the video decoding circuit 21 and thecaption signal data decoded by the graphics circuit 25 are mixed in amixer (not shown in the attached drawings), and then the mixed data isconverted into analog signals by a video digital/analog converter 23,which is displayed after being adjusted into broadcasting signals in aNTSC/PAL encoder 31. In the similar manner, the audio data decoded bythe audio decoding circuit 27 is converted into analog signals by aaudio digital/analog converter 29, which audio data is then synchronizedwith the video signals and output.

[0012] The operation of the conventional reproduction apparatus of theoptical disc will be described in the following.

[0013] The video/audio data recorded in the DVD is composed of user dataand system data. The user data is composed of video data formatted inVBR format which will be processed in the video decoding circuit 21, andaudio data which will be processed in the audio decoding circuit 27. Thesystem data is composed of information relating to systematic functions,by which, for example, the video/audio data selected by the user areread from the DVD and transmitted to the audio decoding circuit 27 andvideo decoding circuit 21 at a suitable rate.

[0014]FIG. 2 shows a conventional DVD format. As shown in FIG. 2, theuser data recorded in the DVD 1 is composed of the video data and theaudio data. By comparison, the recording capacities of the video dataand the audio data are arranged such that about 9 frames of the videodata are recorded for every one frame (1536 bytes) of audio data. Thedisparity between audio and video data stored on the disc is aconsequence of the disproportionate size of audio and video frames. Thevideo data includes, for example, data corresponding to moving imageswhich generally occupies much more space to than the audio data.

[0015] When reproduced from the DVD, the video data and the audio dataare adequately amplified. The amplified signals being corrected in theerror correcting circuit 7 before being temporarily stored in the VBRbuffer 9.

[0016] The signals output from the VBR buffer 9 are input into the datadecoding unit 20 under the control of the navigator 17, and the datadividing operation is executed in at least one of the decoding circuitsof data decoding unit 20. Then, the divided signals are decoded,respectively, by the following process.

[0017]FIG. 3A is a detailed circuit diagram of the video decodingcircuit 21 illustrated in FIG. 1.

[0018] The video decoding circuit 21 comprises a parser 33, a videodecoding unit 35 and a memory 37. The parser 33 receives the bit streamfrom the VBR buffer 9 via a first input terminal and the data dividingcontrol signals from the navigator 17 via a second input terminal. Theparser 33 extracts only the video data in accordance with the datadividing control signals, and outputs the video data to the videodecoding unit 35. Other video-related signals will be parsed tosubsequent stages (such as, the graphics circuit 25 and audio decodingcircuit 27). The video decoding unit 35 generates original signals bydecoding the video data extracted in the parser 33. The video decodingunit 35 may also temporarily store the decoded data of the originalsignal in the memory 37, and output the original signals stored in thememory 37. The video decoding unit comprises a control unit (not shownin the attached drawings) for monitoring the storage volume of the datastored in the memory 37, and for outputting a data transmitting requestsignal to the navigator 17 based on the storage volume of the datastored in memory 37.

[0019] In other words, the video decoding circuit 21 decodes the videodata input from the parser 33, temporarily stores the decoded video datain the memory 37, and outputs signals based on stored data when the datacorresponding to a predetermined screen portion are stored. The videodecoding circuit 21 also monitors the storage volume of the data storedin the memory 37, in which the data decoded in the video decoding unit35 are stored. So long as there is memory space in the memory 37, thevideo decoding unit 35 will decode additional video data by outputtingthe data transmitting request signal to the navigator 17. However, ifthe memory 37 is full, the video decoding unit 35 adjusts the input ofvideo data to memory 37 by outputting a data transmitting stoppingsignal to the navigator 17.

[0020]FIG. 3B is the detailed circuit diagram of the audio decodingcircuit 27 included in the conventional device illustrated in FIG. 1.The audio decoding circuit 27 comprises a parser 39, an audio decodingunit 41 and a memory 43. The parser 39 receives the bit stream from thevideo decoding circuit 21 via a first input terminal, and receives thedata dividing control signal from the navigator 17 via a second inputterminal. The parser extracts only the audio data in accordance with thedata dividing control signals. Thereafter, the audio decoding unit 41decodes the audio data extracted by the parser 39, and temporarilystores the audio data decoded in the memory 43. In other words, theaudio decoding circuit 27 decodes the audio data input via the parser39, temporarily stores the decoded data in the memory 43, andcontinuously outputs the data stored in the memory 43.

[0021] Unlike the video decoding circuit 21, the audio decoding circuit27 does not have any means to output a data transmitting request signalor data transmitting stopping signal to the navigator 17. That is, inthe conventional reproduction apparatus for the optical disc, the rateat which the data is input into the audio decoding circuit 27 isadjusted only according to the storage volume of the data stored in thememory 37 of the video decoding circuit 21 used to decode the videodata.

[0022] As mentioned earlier, the size of recorded video data is about 9times that of recorded audio data, as shown in FIG. 2. The memories 37and 43 are therefore pre-set so that the ratio of the space of thememory 37 in the video decoding circuit 21 and that of the memory 43 inthe audio decoding circuit 27 is also about 9:1. However, audio data isirregularly recorded at various positions on the DVD, and the decodingoperation of the video decoding circuit 21 is not always synchronizedwith the decoding operation of the audio decoding circuit 27. Therefore,if the audio signal data is input into the audio decoding circuit 27depending on the video decoding circuit 21, audio signals outputted canbecome discontinuous.

[0023] In order to overcome the above problem, the memories 37 and 43may be designed so that the ratio of recording space in the memory 37 ofthe video decoding circuit 21 to the recording space in the memory 43 ofthe audio decoding circuit 27 is less than 9:1. To achieve this reducedproportion without sacrificing video data memory capacity, the memory 43of the audio decoding circuit 27 must be made larger. However, in suchcase, the cost of the apparatus rises and the memory 43 can not be usedefficiently.

[0024] In addition, since the audio decoding circuit 27 can not generatethe data transmitting request and stopping signals independently, theconventional apparatus has another problem in that overflow and/orunderflow of the data occurs in the memory 43 of the audio decodingcircuit 27.

[0025] As shown in FIG. 4A, the length of one frame of the normal audiodata being input into the audio decoding circuit 27 is 1536 bytes. Theaudio decoding circuit 27 in the conventional reproduction apparatus, asshown in FIG. 2, therefore processes the audio data one frame (1536bytes) at a time. More specifically, before recording the data in theDVD, audio signals are processed (e.g. encoding the audio data orinserting the error correction code in the audio data, etc.) inincrements of 1536 bytes. Therefore, the audio decoding circuit 27 alsohas to perform the data processing operation per 1536 bytes.

[0026] However, as shown in FIGS. 4B and 4C, the length of the audiodata read from the optical pick-up apparatus 3 may be larger or smallerthan the normal length (1536 bytes) due to a disc error or a recordingerror. In these situations, a further problem will occur since the audiodecoding circuit 27 does not decode the audio signal data normally,causing error signals to be generated as described hereinafter.

[0027] If the size of the bit stream of the audio data being input intothe audio decoding circuit 27 is smaller than 1536 bytes (refer to FIG.4B), some data of the audio data bit stream of a subsequent frame willbe processed together with the data of the present frame, causing errorsto be generated. Also, if the bit stream input is larger than 1536 bytes(refer to FIG. 4C), the remaining data after the 1536th byte in thepresent frame will be processed with the data of the subsequent frame.In both cases, the decoding operation of the audio data can not beperformed normally.

SUMMARY OF THE INVENTION

[0028] It is an object of the present invention to solve theabove-mentioned problems with the conventional reproduction apparatus ofthe DVD.

[0029] It is also an object of the present invention to provide anapparatus and method for compensating reproduced audio signals of theoptical disc by which the memory in the audio decoding circuit can beused most efficiently.

[0030] It is another object of the present invention to provide anapparatus and method for compensating reproduced audio signals of theoptical disc which result from invalid audio data input due, e.g., todisc errors, to reproduce a good quality sound.

[0031] One aspect of the present invention is a method and apparatus forcompensating invalid audio signals by determining whether an audio dataunit has a size that is equal to a predetermined size that is related toa size of a valid audio frame, changing the size of the audio data unitto the predetermined size when it is not equal to the predeterminedsize, and storing the audio data unit into an audio memory. To determinewhether an audio data unit has a size that is equal to a predeterminedsize, header data within the audio data unit is detected, and a size ofthe audio data unit following the detected header is compared to thepredetermined size.

[0032] When the audio data unit is smaller than the predetermined size,the size of the audio data unit may be changed by adding dummy data tothe audio data unit. The dummy data may be muted signal data, or datathat is representative of audio data included in audio data unitspreviously stored in the audio memory. By contrast, when the audio dataunit is larger than the predetermined size, a portion of the audio dataunit exceeding the predetermined size may be eliminated, or it may bestored and overwritten with valid audio data unit.

[0033] Another aspect of the present invention is a method and apparatusfor compensating invalid audio signals by counting a number of bitsfollowing a header of an audio data unit, detecting a size of the audiodata unit based on the number of bits counted in the counting step, andcontrolling storage of the audio data unit into an audio memory based onthe detected size. When the detected size is smaller than apredetermined size, the storage of the audio data unit is controlled bygenerating dummy data, and adding the dummy data to the audio data unitor replacing the audio data unit with the dummy data. As such, storageof the audio data unit into the memory is prevented when the detectedsize is smaller than a predetermined size. By contrast, when thedetected size is larger than a predetermined size, at least a portion ofaudio data corresponding to the audio data unit exceeding thepredetermined size is prevented from being stored in the audio memory.In this manner, consecutively received audio data units are storedseparately.

[0034] Yet another aspect of the present invention is a method andapparatus for controlling storage of audio data to an audio memory basedon amount of data stored in that audio memory. Specifically, the methodand apparatus detect an amount of data stored in the audio memory, andcontrolling storage of audio data into the audio memory based on theamount of data stored. The detecting step includes determining whetherthe amount of data stored in the audio memory is less than apredetermined lower threshold, or greater than a predetermined upperthreshold. This can be accomplished by detecting an address of a lastaudio data unit stored in the memory and comparing that detected addressto the predetermined upper and lower thresholds.

[0035] If the detected address is less than the predetermined lowerthreshold, additional audio data may be requested for storage into theaudio memory. If additional audio data is not available, data that isrepresentative of previously stored audio data. By contrast, if thedetected address is greater than the predetermined upper threshold, adata transmission stopping signal is generated and storage of additionalaudio data may be stored in the memory is halted.

[0036] Further scope of applicability of the present invention willbecome apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of example only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and other objects, features and advantages of thepresent invention will become apparent from the following detaileddescription with the accompanying drawings, which are given by way ofillustration only and thus are not limitative of the present invention,and in which:

[0038]FIG. 1 is a block diagram of a conventional reproduction apparatusof an optical disc;

[0039]FIG. 2 is a diagram of memory space configured for a conventionalDVD system;

[0040]FIG. 3A is a block diagram showing the video decoding circuit 21illustrated in FIG. 1;

[0041]FIG. 3B is a block diagram showing the audio decoding circuit 27illustrated in FIG. 1;

[0042]FIG. 4A shows the formation of normal audio data having a sizecorresponding to one normal frame;

[0043]FIG. 4B shows the formation of invalid audio data having a sizesmaller than one normal frame;

[0044]FIG. 4C shows the formation of invalid audio data having a sizelarger than one normal frame;

[0045]FIG. 5 is a block diagram of the reproduction apparatus of theoptical disc according to the present invention;

[0046]FIG. 6 is an internal block diagram showing an audio decodingcircuit 127 illustrated in FIG. 5;

[0047]FIG. 7 is a detailed block diagram showing an audio decoding unit141 illustrated in FIG. 6;

[0048]FIG. 8 is an internal block diagram showing a data storage volumedetecting unit 153 illustrated in FIG. 7;

[0049]FIG. 9 is a detailed block diagram showing an control unit 155illustrated in FIG. 7, according to a first preferred embodiment of thepresent invention;

[0050]FIG. 10 is a state diagram showing a memory 143 illustrated inFIG. 6;

[0051]FIG. 11 is a flow chart for the method of compensating reproducedaudio signals in the audio decoding circuit 127, according to thepresent invention;

[0052]FIG. 12 is a flow chart showing an invalid data processing routineillustrated in FIG. 11;

[0053]FIG. 13 is a flow chart showing an overflow processing routineillustrated in FIG. 11;

[0054]FIG. 14 is a flow chart showing an underflow processing routineillustrated in FIG. 11;

[0055]FIG. 15 shows a selective preferred embodiment of an audiodecoding unit 141 according to the present invention when the overflowor underflow is generated in the memory 143;

[0056]FIG. 16 shows a selective preferred embodiment of the control unit155 according to the present invention illustrated in FIG. 7; and

[0057] FIGS. 17A-17F are diagrams showing output waveforms of invalidand compensated audio signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058]FIG. 5 is a block diagram of the reproduction apparatus for anoptical disc according to the present invention. As shown in FIG. 5, theoptical disc reproduction apparatus of the present invention comprises:a DVD 101 on which video/audio signals are recorded; a motor 111 forrotating the DVD 101; an optical pick-up apparatus 103 for reading thesignals recorded on the DVD 101; a servo-circuit 113 for driving themotor 111 and the optical pick-up apparatus 103; and a high frequencyamplifying circuit 105 for amplifying the signals read from the opticalpick-up apparatus 103.

[0059] The reproduction apparatus of the present invention alsocomprises: a micro-processor 115 or other processing device for managingthe overall operation of the apparatus upon user's demand, and forcontrolling the operation of the servo-circuit 113 and the highfrequency amplifying circuit 105; and a navigator 117 for receivingcontrol signals from the micro-processor 115 and for controlling datatransmission.

[0060] Further, the reproduction apparatus of the present inventioncomprises: an error correcting circuit 107 for correcting errors of bitstream signals output from the high frequency amplifying circuit 105 andfor outputting corrected signals under the control of the navigator 117;and a VBR buffer 109 for temporarily storing the signals output from theerror correcting circuit 107 under the control of the navigator 117. TheVBR buffer 109 may be a First In First Out (FIFO) buffer.

[0061] In addition, the reproduction apparatus of the present inventioncomprises a data decoding unit 120 which includes a video decodingcircuit 121, a graphics circuit 125 and an audio decoding circuit 127.The bit stream signals output from the VBR buffer are input into thenavigator 117 and the data decoding circuit unit 120. The video decodingcircuit 121 extracts only video signals from the bit stream signalsinput, and decodes them upon receiving data dividing control signalsfrom the navigator 117. Similarly, the graphics circuit 125 extracts anddecodes only caption signals, and the audio decoding circuit 127extracts and decodes only audio signals.

[0062] The audio signal data is decoded into audio data by audiodecoding circuit 127 using the above described process, and the audiodata is converted into audio analog signals which are outputsynchronously with the video signal by an audio digital/analog signalconverter 129. Video data decoded in the video decoding circuit 121 andcaption data decoded in the graphics circuit 125 are mixed in a mixer(not shown in the attached drawings). The mixed signal output by themixer is converted into an analog signal by a video digital/analogsignal converter 123. The analog signals are adjusted to broadcastingsignals in a NTSC/PAL encoder 131 before being output for display.

[0063] The video decoding circuit 121 and the audio decoding circuit 127are both capable of outputting data transmitting request signals to thenavigator 117. The storage of data in the memory included in the videodecoding circuit 121 and the audio decoding circuit 127 may be adjustedbased on the size of those respective memories.

[0064] The video decoding circuit 121 may use its memory mostefficiently by outputting the data transmitting request signals to thenavigator 117 based on the storage volume of the video data recordedtherein.

[0065]FIG. 6 is an internal block diagram showing the audio decodingcircuit 127 of the present invention which is also able to output thedata transmitting request signals according to the present invention.

[0066] According to FIG. 5, the audio decoding circuit 127 preferablyoutputs the data transmitting request signal to the navigator 117.

[0067] The audio decoding circuit 127 of the reproduction apparatus ofthe present invention comprises a parser 139, an audio decoding unit 141and a memory 143. The parser 139 receives a bit stream from the VBRbuffer 109 via a first input terminal and the data dividing controlsignals from the navigator 117 via a second input terminal. The bitstream may be received from VBR buffer 109 directly, or after beingpassed through one or more of video decoding circuit 121 and graphicscircuit 125, as shown in FIG. 5. Parser 139 extracts audio data from thebit stream based on the data dividing control signal from navigator 117,and outputs that extracted audio signal to the audio decoding unit 141.The parser 139 of audio decoding circuit 120 passes other, non-extractedsignals.

[0068] The audio decoding unit 141 within audio decoding circuit 120generates audio data which corresponds to the original audio signals bydecoding the audio signals extracted by the parser 139. The audiodecoding unit 141 also executes data read/write operations. For example,the audio decoding unit 141 may temporarily write the audio data in thememory 143, or it may read and output the audio data recorded in thememory 143. The audio decoding unit 141 may also monitor the storagevolume of the audio data stored in the memory 143 and output the datatransmitting request signals to the navigator 117 accordingly.

[0069]FIG. 7 is a detailed block diagram showing the audio decoding unit141 illustrated in FIG. 6. The audio decoding unit 141 may comprise abit stream analyzing unit 151 for receiving and analyzing the bit streamoutput from the parser 139; and a data storage volume detecting unit(DSVDU) 153 for detecting the storage volume of the audio data stored inthe memory 143 which includes audio data analyzed in the bit streamanalyzing unit 151.

[0070] The audio decoding unit 141 may also comprise a control unit 155for acknowledging the storage volume of the audio data stored in thememory 143 upon receiving signals output from the data storage volumedetecting unit 153, and for outputting an audio data transmittingrequest signal or an audio data transmitting stopping signal to thenavigator 117 based on the acknowledged storage volume. The control unit155 also determines whether the audio data being analyzed in the bitstream analyzing unit 151 is invalid data or normal data. Thisdetermination can be made by, e.g., counting the number of bytesincluded in the received audio data and comparing that number to anumber of bytes in a normal audio data unit. The control unit 155controls the read/write operation of the audio data output from the bitstream analyzing unit 151 in accordance with the storage volume of theaudio data of the memory 143. The control unit 155 also controls theoperations of other circuit subunits (not shown in the attacheddrawings) included in the audio decoding unit 141.

[0071] Under the control of the control unit 155, the audio data of onenormal frame being output from the memory 143 is decoded by amultiplexer 157 and an Inverse Discrete cosine ConverTing unit (IDCT)159 according to the time-frequency converting method, and then thedecoded audio data is output. As seen in FIG. 5, the audio signal dataoutput through the IDCT 159 is converted by the audio digital/analogsignal converter 129 into audio analog signals, which are output througha speaker or other audio output device (not shown in the attacheddrawings).

[0072] In other words, the audio decoding unit 141 adjusts the ratewhich the audio signals are being input thereto. Audio decoding unit 141is therefore able to decode the audio signals typically associated withone normal frame by generating the data transmitting request signal orthe data transmitting stopping signal based on the bytes countingoperation performed by the control unit 155, and by acknowledging thestorage volume of the audio data stored in the memory 143 in accordancewith the detecting signal of the data storage volume detecting unit 153.

[0073]FIG. 8 is an internal block diagram showing the data storagevolume detecting unit 153 illustrated in FIG. 7. As shown in FIG. 8, thedata storage volume detecting unit 153 comprises: a last addressdetecting unit 161 for detecting the last address stored in the memory143; a reference address storage means 163 for storing a referenceaddress which will be compared with the last address stored in thememory 143 to detect an overflow/underflow; a comparing unit 165 forcomparing an address detected by the last address detecting unit 161with the reference address stored in the reference address storage means163; and an overflow/underflow detecting unit 167 for detecting theoverflow/underflow of the memory 143 based on the comparison of thecomparing unit 165. The subunits of the data storage volume detectingunit 153 may be implemented as software as well as hardware.

[0074] The detecting operation of the storage volume of the data storedin the memory 143 by the data storage volume detecting unit 153 is nowdescribed with reference to FIG. 8. The comparing unit 165 compares thelast address detected by the last address detecting unit 161 with thereference address of the reference address storage unit 163, and outputsan comparing signal used to control whether the overflow/underflowdetecting unit 167 outputs an overflow/underflow state signal.

[0075]FIG. 9 is a detailed block diagram showing the control unit 155illustrated in FIG. 7. As shown in FIG. 9, the control unit 155comprises: a counter 181 for counting bytes of the audio data outputfrom the bit stream analyzing unit 151; a header data detecting unit 183for detecting the header data from the audio data output from the bitstream analyzing unit 151; and an invalid data detecting unit 185 fordetecting invalid data by based on the result of the counter 181 and theheader data detecting unit 183.

[0076] The control unit 155 further comprises a Central Processing Unit(CPU) 187 for controlling a read/write operation into both a dummy datagenerating unit 189 and the memory 143 based on output signals of theinvalid data detecting unit 185. Also, the CPU 187 outputs the datatransmitting stopping signal or the data transmitting request signal tothe navigator 117 in response detection of an overflow/underflow byDSVDU 153.

[0077] When the audio signal detected in the invalid data detecting unit185 is less than one normal frame (1536 bytes), the CPU 187 controls thedummy data generating unit 189 to generate dummy data which is stored inthe memory 143 to make a complete normal frame. That is, by mixing thedummy data, the length of the input audio signal is adjusted into onenormal frame.

[0078] On the other hand, when the audio signals detected in the invaliddata detecting unit 185 is longer than one normal frame, the CPU 187turns off data writing into the memory 143, effectively preventing anyaudio signals beyond one normal frame (1536 bytes) to be written fromthe bit stream analyzing unit 151 into the memory 143. Selectively, ifthe audio signals beyond one normal frame (1536 bytes) are alreadywritten, the CPU 187 may control the memory 143 so that the audiosignals are overwritten by the audio signals of the next frame.

[0079]FIG. 10 is a state diagram showing the memory 143 of the audiodecoding circuit 127 illustrated in FIG. 6. The reference addressstorage unit 163 (shown in FIG. 8) stores the reference addressescorresponding to the underflow point and overflow point, which addressesdepend on the size of the memory 143. The overflow/underflow detectingunit 167 outputs an overflow state signal when the address of the lastdata stored in the memory 143 is over the reference addresscorresponding to the overflow point, and an underflow state signal whenthe last address of the data stored in the memory 143 is under thereference address corresponding to the underflow point.

[0080] According to the overflow/underflow state signal detected fromthe overflow/underflow detecting unit 167, as shown in FIG. 8, thecontrol unit 155 outputs the data transmitting stopping signal/datatransmitting request signal. Undesired errors, which are otherwisegenerated by the memory 143 of the audio decoding circuit 127, aretherefore prevented. Consequently, the memory 143 can be used mostefficiently.

[0081] In the following, the method for compensating the reproducedaudio signals of the optical disc according to the present inventionwill be described in detail.

[0082] As shown in FIG. 2, the DVD 1 records user data composed of thevideo/audio data, and system data used during the reproduction of theuser data. With reference to FIG. 5, these data are read and reproducedas signals by the optical pick-up apparatus 103. The reproduced signalsare output after being amplified in the high frequency amplifyingcircuit 10. The signals output from the high frequency amplifyingcircuit 105 are corrected by ECC 107, and output to VBR buffer 109 wherethey are temporarily stored.

[0083] The VBR buffer 109 generates a bit stream based on the signalstemporarily stored therein. The bit stream is input from VBR buffer 109into the navigator 117 and data decoding circuit unit 120. Navigator 117decodes the signals of the system data and then executes the datadividing controlling operation. That is, the navigator 117 controls thedata decoding circuit unit 120 so that the bit stream is decoded by thevideo decoding circuit 121 if the input bit stream represents the videodata, and the bit stream is decoded by the audio decoding circuit 127 ifthe bit stream represents audio data. Similarly, the bit stream isdecoded by the graphics circuit 125 if the bit stream represents captiondata.

[0084] With reference to the audio decoding circuit 127 in FIG. 6, theaudio decoding unit 141 in FIG. 7 and the control unit 155 in FIG. 9,the extracting operation of the audio decoding circuit 127 and itssignal-processing operation will be explained.

[0085] First, the navigator 117 determines the types of signalsrepresented by the bit stream input from VBR buffer 109. When thesignals in the bit stream represent the audio data, the navigator 117controls the audio decoding circuit 127 to input the bit stream receivedby the parser 139 of the audio decoding circuit 127 into the audiodecoding unit 141. The audio data being input into the audio decodingunit 141 is analyzed in the bit stream analyzing unit 151, and thenstored in the memory 143.

[0086] In the above process of reproducing the optical disc, the datastored on the optical disc is processed in units of frames. When theaudio data is being stored in the memory 143, the control unit 155determines whether the reproduced signals of the audio data signalshaving the length of one normal frame. If the length of the reproducedsignals of the audio data is not of normal length (i.e., is not 1536bytes), the control unit 155 executes the operation for compensating thelength of the reproduced audio signals to adjust the reproduced signalsto signals is of one normal frame.

[0087]FIG. 11 is a flow chart illustrating the method for compensatingthe reproduced audio signals in the audio decoding circuit 127 accordingto the present invention. FIG. 12 is a flow chart showing the method ofprocessing of the invalid data illustrated in FIG. 11. FIG. 13 is a flowchart showing the method of processing an overflow condition illustratedin FIG. 11. FIG. 14 is a flow chart showing the method of processingaccording to an underflow illustrated in FIG. 11.

[0088] As shown in FIG. 11, the initial value of the bytes counter 181is set to ‘0’ (zero) (step 1101), and the header data detecting unit 183detects header data from audio data output by bit stream analyzing unit151 (step 1103).

[0089] As illustrated in FIG. 2, one frame of audio data typicallyincludes 1536 bytes of data, including header data, user data and anerror correcting codes (e.g., Cyclic Redundancy Code:CRC). The headerdata is placed before the user data which may be either one of thevideo/audio signals, and the user audio data is placed after the headerdata. Thus, the detection of the header data may be used to determinebeginning of the one frame of audio data.

[0090] When the header data is detected in step 1103, the bytes counter181 counts the bytes of the data being output by the bit streamanalyzing unit 151 (step 1105), and the memory 143 stores the audio dataoutput by the bit stream analyzing unit 151 (step 1107).

[0091] The steps of counting the bytes of the audio data received fromVBR buffer 109 and of concurrently storing that audio data in the memory143 (steps 1105 and 1107) are repeatedly executed until the header dataof next frame is detected by the header data detecting unit 183 (step1109).

[0092] Referring again to FIG. 9, the bytes counter 181 and header datadetecting unit 183 send data to CPU 187 via invalid data detecting unit185. In addition, bytes counter 181 transmits a counting result, andheader data detecting unit 183 transmits a detecting signal. The invaliddata detecting unit 185 detects whether the audio data input is invaliddata or normal data by counting the bytes of the data input until theheader data of the next frame is detected (step 1111), normal datahaving a length equal to one normal frame (1536 bytes).

[0093] If the number of bytes in a frame of audio data is determined bycounter 181 to exceed 1536 bytes in said step 1111, the audio data isdetermined to be invalid data. When the audio data is determined to beinvalid, it is processed by the CPU 187 (step 1113). In other words, theprocessing of the invalid data in the step 1113 will be executed whenthe length of the one frame of the audio data input is not 1536 bytes.

[0094]FIG. 12 shows the processing of the invalid data illustrated inFIG. 11. While processing invalid data, it is first determined whetherthe invalid frame of audio data received from VBR buffer 109 is largeror smaller than 1536 bytes (step 1201). If it is determined that theinvalid frame of audio data is smaller than 1536 bytes in step 1201, theCPU (refer to FIG. 9) turns off the error correcting code(CRC) in ordernot to execute the correction of errors included in the audio data (step1203). Meanwhile, the CPU 187 controls the dummy data generating unit189 to generate the dummy data, and then stores the generated dummy datainto the memory 143 (step 1205). The dummy data will be repeatedlygenerated and stored until the audio data reaches 1536 bytes.

[0095] On the other hand, if it is determined that the invalid frame ofaudio data is larger than 1536 bytes by step 1201, the CPU (refer toFIG. 9) turns off the error correcting code(CRC) in order not to executethe correction of errors included in the audio data (step 1207).Meanwhile, the CPU counts the audio data input, and removes the datafollowing the 1536th byte (step 1211). The remaining data may be removedby discontinuing writing function to the memory 143 in the step ofstoring the audio data into the memory 143, effectively halting storageof the remaining data in the memory 143. Alternatively, the remainingdata may be removed by overwriting the remaining data with the audiodata of the next frame, if the remaining data has already been stored inthe memory.

[0096] Once the audio data is adjusted so that the length of one frameof the audio data is 1536 bytes in step 1205 or step 1211, theprocessing of the invalid data is terminated, and the reproductionprocess returns to step 1115 in FIG. 11. If the above-describedprocessing of the invalid data is executed, the length of one resultingframe audio data will become one normal frame length (1536 bytes).

[0097] At step 1115, the CPU 187 continuously monitors, during thecourse of storing the audio data in the memory 143, whether an interruptsignal indicating overflow of the memory 143 is input from the datastorage volume detecting unit 153. Additionally, the CPU 187continuously monitors whether an interrupt signal indicating underflowof the memory 143 is input from the data storage volume detecting unit153 (step 1119).

[0098] The overflow and underflow of the memory 143 is detected (in step1115) by the data storage volume detecting unit 153, as shown in FIGS. 7and 8, based on the storage volume of the data stored in the memory 143as follows. First, the last address detecting unit 161 detects theaddress of the last data having been stored in the memory 143, andoutputs the detected last address to the comparing unit 165. Thecomparing unit 165 compares the last address with the referenceaddresses for overflow and underflow, respectively. Theoverflow/underflow detecting unit 167 outputs the interruption signal ofeither overflow or underflow based on the current storage volume of thedata stored in the memory 143. The interruption signal is input into theCPU 187, and according to the respective interruption signal the CPU 187outputs the data transmitting stopping signal or the data transmittingrequest signal to the navigator 117.

[0099] Thus, detection of memory 143 overflow in said step 1115 meansthat excessive data is stored in the memory 143 and that the addressdetected by the last address detecting unit 161 is over the referenceaddress, i.e., the memory 143 has overflowed. Therefore, the CPU 187outputs the data transmitting stopping signal to the navigator 117.

[0100] So long as an interruption signal indicating an overflow of thememory 143 is being output from the data storage volume detecting unit153, the CPU 187 executes an overflow processing routine as indicated bystep 1117. The overflow processing routine of step 1117 is executed whenthe storage volume of the data stored in the memory 143 of the audiodecoding circuit 127 is over a predetermined value.

[0101]FIG. 13 shows, in more detail, the overflow processing routineillustrated in FIG. 11. In that routine, the CPU 187 outputs the datatransmitting stopping signal to the navigator 117 (step 1301). The CPU187 then determines whether the bit stream analyzing unit 151 transmitsany audio data (step 1303). If audio data is transmitted, the CPU 187turns off the writing of the memory 143, thereby inhibiting the writingof the memory with the transmitted audio data (step 1305). If audio datais not transmitted, the CPU 187 examines whether the overflow of thememory 143 continues (step 1307). If the overflow flag of the memory 143remains active, the reproduction process returns to the step 1301, andsteps 1301 to 1307 are repeated.

[0102] While the above-described process is executed, the data storagevolume detecting unit 153 detects the storage volume of the data storedin the memory 143 and outputs state signals to the CPU 187. If it isconcluded that the overflow of the memory 143 is released by the statesignal, the CPU 187 outputs the data transmitting request signal to thenavigator 117. Simultaneously, the writing operation is resumed to storethe audio data being output from the bit stream analyzing unit 151 intothe memory 143 (step 1309). Thus, the processing of the overflow endsand the reproduction process returns to step 1119 in FIG. 11.

[0103] The fact that the memory 143 is underflowed in step 1119 meansthat the address detected by the last address detecting unit 161 is lessthan the reference address for underflow, and there exists an excessamount of vacant storage space in the memory 143. Therefore, theoverflow/underflow detecting unit 167 outputs the interruption signal ofunderflow to the CPU 187, and the CPU 187 outputs the data transmittingrequest signal to the navigator 117. More specifically, if the memory143 is in underflow, the CPU 187 executes the data processing operationaccording to the processing of the underflow processing routine (step1121).

[0104]FIG. 14 shows in more detail the processing of the an underflowsituation illustrated in FIG. 11. The CPU 187, in the initial stage ofthe processing of the underflow, stores the audio data being output fromthe bit stream analyzing unit 151 into the buffer in the unit 151, andupdates the buffer (step 1401). The CPU 187 then outputs the datatransmitting request signal to the navigator 117 (step 1403). The CPU187 determines whether there is any audio data transmitted by said step1403 (step 1405). If audio data is transmitted, the CPU 187 continues tostore the audio data into the memory 143. If no audio data istransmitted, the CPU 187 outputs the data stored in the buffer, whichdata is stored into the memory 143 (step 1407). That is, a portion ofaudio data previously received is redundantly stored in memory 143during an underflow condition if no new data is transmitted.Alternatively, dummy data, a default data pattern, or an average of somegroup of previously transmitted or stored audio data may be stored inmemory 143 under such conditions.

[0105] During the execution of the above-described process, the CPU 187examines whether the underflow condition of the memory 143 remains ornot (step 1409). If the underflow condition remains, the reproductionprocess returns to the step 1401, and said steps 1401 to 1409 arerepeated. While the underflow condition remains without any transmitteddata, the data stored in the buffer is repeatedly output and stored inthe memory 143.

[0106] Once the underflow of the memory 143 is released by the statesignal output from the data storage volume detecting unit 153, the CPU187 clears the buffer (step 1411), and the processing of the underflowends so that the reproduction process returns to step 1123 in FIG. 11.

[0107] The multiplexer 157 and the IDCT 159 are used to decode audiosignals being output from the memory 143 into decoded audio datacorresponding to the original signals based on a time-frequencyconverting method (refer to FIG. 7) (step 1123). The decoded audio datais then output to the audio digital/analog converter 129 (refer to FIG.5). The decoded audio signal data being output from the audio decodingcircuit 127 is then converted into analog signals by the audiodigital/analog converter 129, before being output to the speaker, etc.(not shown in the attached drawings).

[0108]FIG. 15 shows the audio decoding unit 141 of a second preferredembodiment of the present invention. As shown in FIG. 15, the bit streamanalyzing unit 251 analyzes data in the bit stream input from the parser139, the analyzed data being temporarily stored in the memory 143. Thebit stream output from the bit stream analyzing unit 251 is input intothe control unit 255, where the length of the audio data input iscompared with the length of one normal frame. The data storage volumedetecting unit 253 detects the data storage volume of the audio dataoutput from the memory 143, and outputs a state signal according to thedata storage volume detected.

[0109] In accordance with the state signal, the control unit 255generates the audio data transmitting request signal or the audio datatransmitting stopping signal. The audio data output from the memory 143is decoded by the multiplexer 257 and IDCT 259, and the decoded data isoutput.

[0110] The audio decoding unit 141 according to the second preferredembodiment generates a data transmitting request signal if a minimumpredetermined amount of vacant storage space exists in the memory 143,and generates a data transmitting stopping signal if maximumpredetermined amount of vacant storage space does not exist in thememory 143. That is, according to the second preferred embodiment, adata transmitting stopping signal can be sent to the navigator 117 toinhibit the supply of data into the audio decoding circuit 127 when anoverflow condition exists in the memory 143, and a data transmittingrequest signal can be sent to the navigator 117 to request data when anunderflow condition exists in the memory 143. However, the controllingoperation of the audio decoding unit 141 of the first preferredembodiment (FIG. 7), by which the dummy data is directly and repeatedlystored in, or output from, the memory 143, is impossible according tothis preferred embodiment.

[0111]FIG. 16 shows the control unit 155 of a third preferred embodimentof the present invention. As shown in FIG. 16, the control unit 155according to this preferred embodiment comprises: a counter 191 forcounting the bytes of the audio data being output from the bit streamanalyzing unit 151; a header data detecting unit 193 for detecting theheader data from the audio data being output from the bit streamanalyzing unit 151; and an invalid data detecting unit 195 for detectinginvalid data upon receiving detecting signal output from the header datadetecting unit 193.

[0112] Also, the control unit 155 of this preferred embodiment comprisesa Central Processing Unit (CPU) 197 for controlling the read or writeoperation into the memory 143 based on signals output from the invaliddata detecting unit 195, and for outputting a data transmitting stoppingsignal or a data transmitting request signal to the navigator 117according to the overflow/underflow state signal detected in the datastorage volume detecting unit 153.

[0113] No separate dummy data generating unit 189 exist in the controlunit 155 of this preferred embodiment. Therefore the CPU 197 adjustsinvalid data to the normal data having one normal frame length bystoring the data input into the memory 143 previously repeatedly or byinserting the dummy data into the invalid data (refer to FIG. 17C). Inthis regard, the dummy data may be inserted by well-known methods, forexample, by inserting a desirable portion of a sample wave into theinvalid data. It should be obvious to those skilled in the art that thetone quality of the signals according to the above method can be made tobe substantially similar from original signals. When the length of theaudio data input is longer than the length of the data of the one normalframe, as in FIG. 9, the storage of the data exceeding a normal framewill be inhibited.

[0114] FIGS. 17A-17F are diagrams showing the output waveforms ofinvalid data and the compensated audio signals when the invalid data areinput.

[0115] As shown in FIG. 17A, when an invalid data whose length is lessthan the normal length (e.g., 1216 bytes) is input, signals of abnormalwaveforms will be output absent compensation, as shown in FIG. 17B. Thatis, noise occurs at the portion of the signal representing invalid data.

[0116] According to the present invention, invalid data whose length isgreater than the normal length may be monitored and neutralized byeither inhibiting storage of that data into the memory 143 during thewriting operation or by removing that data during the reading operation,as shown in FIG. 17C.

[0117] When invalid data has a length of less than the normal length,the portion of the signal representing invalid data may be replaced withdummy data, muted data, or data representing previously stored data. Ifinvalid data is replaced with muted data, as shown in FIG. 17D, thememory's writing operation will be turned off while the invalid data isinput into the memory 143, so that the invalid data will be replaced bymuted data, e.g., in a signal mute unit (not shown in the attacheddrawings). For instance, such a single mute unit can be used in place ofdummy data generating unit 189 in FIG. 9. That is, instead of storingdummy data using dummy data generating unit 189, a signal muting unitmay be used to store muted data. The muted data may be added to theinvalid audio data before storage of that audio data, the muted data maybe stored in place of the invalid audio data.

[0118]FIG. 17E shows waveform of reproduced audio signals compensated inaccordance with that above-described preferred embodiment of the presentinvention, in which the output of the audio data is adjusted when anunderflow condition is detected by repeatedly outputting the data storedin the memory 143. Also, FIG. 17F shows output waveform of the data towhich a dummy data is added as described previously. For instance, whenthe invalid data is input having a length of 1216 bytes, which issmaller than one normal frame (1536 bytes), this preferred embodiment ofthe present invention adjusts the invalid data to normal length byadding dummy data to the invalid data.

[0119] While there have been illustrated and described what are atpresent considered to be preferred embodiments of the present invention,it will be understood by those skilled in the art that various changesand modifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of the presentinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the presentinvention without departing from the central scope thereof. Therefor, itis intended that the present invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention includes allembodiments falling within the scope of the appended claims.

[0120] The foregoing description and the drawings are regarded asincluding a variety of individually inventive concepts, some of whichmay lie partially or wholly outside the scope of some or all of thefollowing claims. The fact that the applicant has chosen at the time offiling of the present application to restrict the claimed scope ofprotection in accordance with the following claims is not to be taken asa disclaimer or alternative inventive concepts that are included in thecontents of the application and could be defined by claims differing inscope from the following claims, which different claims may be adoptedsubsequently during prosecution, for example, for the purposes of acontinuation or divisional application.

What is claimed is:
 1. A method for controlling an audio memory of anaudio decoding circuit included in a data decoding unit having a videodecoding circuit, said method comprising: detecting an amount of databased on address of a last audio data stored in said audio memory;determining whether said amount of data stored in said audio memory isless than a predetermined lower threshold; and requesting additionalaudio data to be stored into said audio memory independently ofprocessing in the video decoding circuit when said amount of data storedin said audio memory is less than said predetermined lower threshold. 2.The method recited by claim 1 , further comprising: storing data that isrepresentative of previously stored audio data when additional audiodata is not available for storage into said audio memory while saidamount of data stored in said audio memory is less than saidpredetermined lower threshold.
 3. The method recited by claim 1 ,further comprising: storing dummy data into said audio memory while saidamount of data stored in said audio memory is less than saidpredetermined lower threshold.
 4. An apparatus for controlling an audiomemory of an audio decoding circuit included in a data decoding unithaving a video decoding circuit, said apparatus comprising: a volumedetecting unit for detecting an amount of data stored in said audiomemory, said volume detecting unit comprising a last address detectingunit for detecting an address of a last audio data stored in said audiomemory; a comparing unit for determining whether said amount of datastored in said audio memory is less than a predetermined lowerthreshold; and a controller including a signal generator, said signalgenerator generating a data transmission request signal requestingadditional audio data to stored into said audio memory independently ofprocessing in the video decoding circuit when said amount of data storedin said audio memory is less than said predetermined lower threshold. 5.The apparatus recited by claim 4 , wherein said controller stores datathat is representative of previously stored audio data when additionalaudio data is not available for storage into said audio memory whilesaid amount of data stored in said audio memory is less than saidpredetermined lower threshold.
 6. The apparatus recited by claim 4 ,wherein said controller further includes a dummy data generator forgenerating dummy data to be stored in said audio memory while saidamount of data stored in said audio memory is less than saidpredetermined lower threshold.
 7. A method for compensating invalidaudio data units to be stored in an audio memory, said methodcomprising: detecting a size of an audio data unit; comparing thedetected size of audio data unit with a predetermined size; adjustingsize of the audio data unit into a predetermined size based on theresult of the comparing step; and storing the audio data units intoaudio memory in accordance with the adjusting step.
 8. The methodrecited by claim 7 , said adjusting step comprising: generating dummydata when detected size is smaller than said predetermined size based onthe comparing step; and adding said dummy data to said audio data whensaid detected size is smaller than said predetermined size.
 9. Themethod recited by claim 7 , wherein said adjusting step removes at leasta portion of said audio data unit when said detected size is larger thansaid predetermined size based on the comparing step, said portioncorresponding to audio data unit exceeding said predetermined size. 10.The method recited by claim 7 , wherein said storing step stores onlythe audio data units corresponding to the predetermined size when saiddetected size is larger than said predetermined size based on thecomparing step.
 11. The method recited by claim 7 , further comprising:counting a number of bits following a header of said audio data unit,wherein said detecting step includes detecting said size of said audiodata unit based on said number of bits counted in said counting step.12. An apparatus for compensating invalid audio data units to be storedin an audio memory, said apparatus comprising: a detecting unit fordetecting a size of an audio data unit; a comparing unit for comparingthe detected size of audio data unit with a predetermined size; and acontrol unit for adjusting the detected data into a predetermined sizebased on the comparing result of the comparing unit, buffer memory forstoring the audio data units in accordance with control of the controlunit.
 13. The apparatus recited by claim 12 , said control unitcomprising: a dummy data generating unit for generating dummy data whensaid detected size is smaller than said predetermined size in accordancewith the comparing of the comparing unit, said dummy data being added tosaid audio data unit when said detected size is smaller than saidpredetermined size.
 14. The apparatus recited by claim 12 , wherein saidcontrol unit controls said buffer memory to not store said audio datawhen said detected size is smaller than said predetermined size.
 15. Theapparatus recited by claim 14 , wherein said control unit controls saidbuffer memory to store dummy data in place of said audio data unit whensaid detected size is smaller than said predetermined size.
 16. Theapparatus recited by claim 12 , wherein said control unit controls thebuffer memory to prevent storage of said audio data unit when saiddetected size is larger than said predetermined size.
 17. The apparatusrecited by claim 12 , wherein said control unit controls the buffermemory to prevent storage of a least a portion of said audio data unitwhen said detected size is larger than said predetermined size, saidportion corresponding to audio data unit exceeding said predeterminedsize.
 18. The apparatus recited by claim 12 , wherein said control unitcontrols said buffer memory to store consecutively received audio dataunits separately.
 19. The apparatus recited by claim 12 , furthercomprising: counter for counting a number of bits following a header ofsaid audio data unit, wherein said detecting unit detects said size ofsaid audio data unit based on said number of bits counted by saidcounter.
 20. A method for controlling an audio memory of an audiodecoding included in a data decoding unit having a video decodingcircuit, said method comprising: detecting an amount of data stored insaid audio memory by detecting an address of a last audio data stored insaid audio memory; determining whether said amount of data stored insaid memory is greater than a predetermined upper threshold; andgenerating a data transmission stopping signal independently ofprocessing in the video decoding circuit when said amount of data storedin said audio memory is greater than said predetermined upper thresholduntil said amount of data stored in said audio memory is less than orequal to said predetermined upper threshold.
 21. The method recited byclaim 20 , further comprising: halting storage of additional audio datain said memory when said amount of data stored on said memory is greaterthan said predetermined upper threshold.
 22. An apparatus forcontrolling an audio memory of an audio decoding circuit included in adata decoding unit having a video decoding circuit, said apparatuscomprising: a volume detecting unit for detecting an amount of datastored in said audio memory, wherein said volume detecting unitcomprising a last address detecting unit for detecting an address of alast audio data stored in said audio memory; a comparing unit fordetermining whether said amount of data stored in said audio memory isgreater than a predetermined upper threshold; and a controller includinga signal generator, said generator generating a data transmissionstopping signal independently of processing in the video decodingcircuit when said amount of data stored in said audio memory is greaterthan said predetermined upper threshold until said amount of data storedin said audio memory is less than or equal to said predetermined upperthreshold.
 23. The apparatus recited by claim 22 , wherein saidcontroller halts storage of additional audio data in said memory whensaid amount of data stored on said memory is greater than saidpredetermined upper threshold.
 24. A method for processing an invalidaudio data units, said method comprising: storing an audio data unitsinto audio buffer memory; detecting a size of the audio data unit;comparing the detected size of audio data unit with a predeterminedsize; adjusting size of the audio data unit into a predetermined sizebased on the result of the comparing step; and processing the adjustedaudio data unit.
 25. The method recited by claim 24 , wherein saidadjusting step comprising: generating dummy data when detected size issmaller than said predetermined size based on the comprising step, andadding said dummy data to said audio data when said detected size issmaller than said predetermined size.
 26. The method recited by claim 24, wherein the adjusting step comprising: removing at least a portion ofsaid digital data unit when said detected size is larger than saidpredetermined size based on the comparing step, said portioncorresponding to digital data unit exceeding said predetermined size.27. The method recited by claim 24 , wherein said processing stepcomprising: decoding only the audio data unit corresponding to thepredetermined size when the detected size is larger than thepredetermined size based on the comparing step.
 28. A method forcompensating an invalid digital data unit, said method comprising:counting a number of bits in said digital data unit; comparing thedetected number of digital data unit with predetermined number; andcompensating the detected number into the predetermined number based onthe comparing result.
 29. The method recited by claim 28 , wherein thecounting step counts a number of bits following a header of said digitaldata unit.
 30. The method recited by claim 28 , further comprising:processing the compensated digital data units.
 31. The method recited byclaim 30 , wherein the processing step comprising: processing only thenumber of digital data corresponding to the predetermined number whendetected number is larger than said predetermined number based on thecomparing step.
 32. The method recited by claim 30 , wherein theprocessing step includes storing only the number of digital datacorresponding to the predetermined number when detected number is largerthan said predetermined number based on the comparing step; and decodingthe stored digital data.
 33. The method recited by claim 28 , whereinthe compensating step comprising: generating a dummy data when detectednumber is smaller than said predetermined number based on the comparingstep; and adding said dummy data to said digital data when said detectednumber is smaller than said predetermined number.
 34. The method recitedby claim 28 , wherein the compensating step comprising: removing atleast a portion of said digital data unit when said detected size islarger than said predetermined size based on the comparing step, saidportion corresponding to digital data unit exceeding said predeterminedsize.